The approaches should usually arm automatically.

Within 30nm and approach loaded into the database are the
triggers.

Won't go active unless a slew of conditions are
met including RAIM.

Don't know about the 300, but the 89B, same vintage,
sometimes had to be manually armed.

Never understood why that was. Would
guess that it would have to be armed 2 mi outside the
FAF for success.

Doesn't really answer your question... sorry. Bill Hale